Field of the Invention
This invention relates generally to tinted or colored glass and, in one particular embodiment, to a method of making colored glass in a float glass process.
Technical Considerations
In a typical float glass process, glass batch materials are melted in a glass furnace to produce a glass melt. The glass melt is poured onto a bath of molten metal, typically tin, in a float bath. The glass melt is drawn across the top of the molten tin to form a dimensionally stable float glass ribbon.
To form a colored glass sheet, one or more colorant materials are added to the glass batch materials. For example, the primary colorant in green colored glass compositions is iron, which can be present in ferric (Fe2O3) and ferrous (FeO) forms. Other common colorants include transition or rare earth metal oxides such as cobalt, nickel, chromium, manganese, and titanium, erbium, neodymium, and selenium in its elemental or ionized states, depending on the desired color of the glass sheet. These colorants are added to the glass batch material and become homogeneously dissolved throughout the resultant piece of glass.
In producing conventional colored glass, the relative amounts of these colorants is closely monitored and controlled within an operating range to provide the glass with the desired color and spectral properties for a particular use. Varying the colorants outside of this operating range or inadequately melting these colorants in the glass melt can detrimentally effect the final color and light transmittance characteristics of the glass as well as the melting qualities of the glass composition. Additionally, some blue or green colored glass compositions contain selenium as one of the major colorants. However, a problem with selenium is that it is highly volatile at the temperature is used for conventional glass manufacture. The selenium can rapidly volatilize before it can be incorporated into the glass and can thus affect the final glass color. Selenium volatilization can also lead to other production problems, such as, unacceptable furnace emissions, color streaks, and poor color control.
If more than one color of glass is in production, a separate furnace is required for each glass melt composition. This increases the capital investment required and makes color changes difficult. Alternatively, in the same furnace, it takes days or more than a week to change glass color from one to another, during which process hundreds of tons of out-of-color specification glass might be discarded or recycled. This glass color change process can be particularly long if it involves changing from an intensely colored product to a lightly colored product.
Therefore, it would be advantageous to provide a method of making colored float glass that eliminates or reduces at least some of the problems described above.